It is well known in the color photography art that color images are produced by a color dye which is formed by a coupling reaction between an oxidized product of an aromatic primary amine color developing agent and a coupler. Various types of cyan, magenta and yellow dye- forming couplers are well known for use in such coupling reactions. The couplers are often used in combination with one or more solvents and/or other additives. For example, the Aoki et al. U.S. Pat. No. 4,686,177 discloses silver halide color photographic materials containing a cyan coupler which may be dissolved in an organic solvent. Aoki et al. broadly disclose numerous organic solvents which may be employed. Japanese reference No. 61-51063 discloses compositions in which a coupler is dissolved in an organic solvent such as dimethylsulfoxide.
It is often desirable in color photography to provide the coupler compounds with improved properties, for example with improved coupler activity, i.e., improved colorability as indicated by the acceleration of the reaction of the coupler with the oxidized developer in forming the color dye and/or by an increase in the color density of the resulting color dye. It is also desirable to provide the dye which is formed from the reaction of the coupler compound with the oxidized developer with improved light stability. For example, the Yamada et al. U.S. Pat. No. 4,113,488 discloses a method for improving the light fastness of a magenta color image by incorporating into a layer containing the magenta color image at least one light fastness improving phenolic compound and at least one synergistic light fastness improving sulfide or sulfoxide compound.
The Takahashi et al. U.S. Pat. No. 4,770,987 discloses silver halide color photographic materials which contain a magenta coupler and an antistain agent in the form of lipophilic fine particles. The antistain agent comprises a sulfone compound and the material is disclosed as preventing stain formation on the non-color developed areas due to aging and the like after processing. The Lischewski et al. U.S. Pat. No. 4,419,431 discloses additional compositions comprising a light-sensitive diazonium compound and a sulfide, sulfoxide or sulfone compound for increasing the light stability of an azo image dye stuff formed by light imaging and development of the composition. The Hirata et al. U.S. Pat. No. 4,758,498 discloses additional photographic compositions including a sulfone compound for preventing fading of and image dye and staining of white background areas.
Many coupler compositions, however, are disadvantageous in that relatively large amounts of a coupler are required to provide satisfactory color density, the reaction rate of the coupler with the oxidized developer is undesirably low, the colored image which is formed from the reaction of the coupler compound with the oxidized developer exhibits unacceptable light instability, and/or the like. Accordingly, a continuing desire exists for coupler compositions of improved activity for use in color photographic materials and methods.
Additionally, various coupler compounds, for example, 2-equivalent pyrazolone magenta couplers, exhibit a phenomenon which is referred to as continued coupling. That is, the couplers often yield high Dmin values when a stop bath is not used between the development and bleach steps of a color photographic process. The continued coupling may be a function of the low "pKa" property of the couplers and reflects the tendency of the couplers to remain significantly ionized under bleaching conditions, thereby allowing reaction with retained developer. Since it is desirable to maintain processing simplicity in color photographic processing by excluding the need for a stop bath, an alternate means of reducing the continued coupling phenomenon without significantly affecting coupler activity is desired.